Various types of head mounted displays are known. An exemplary head mounted display (throughout the following specification the initials “HMD” may be used to mean “head mounted display”) includes optics or optical components such as lenses, mirrors or the like, to form an image generated by an image source to an eye or eyes of a person viewing the image (viewer). The image source develops and/or provides an image intended to be viewed and may or may not be part of the HMD. Head mounted display systems are used in the field of virtual reality, in aircraft, for example, as part of a heads-up display system, and by individuals in the field such as, for example, soldiers or other field operatives.
Many prior head mounted display systems use light emitting sources, such as a cathode ray tube, light emitting diode, etc., to create an image. Several disadvantages to such light sources and head mounted displays using them are relatively large size, heavy weight, and cumbersome nature. For example, in some display systems, counterbalancing weights and support systems are needed to support the helmet containing the image source and optics so that the helmet does not strain the head, neck, shoulders, etc. of the user.
In some prior display systems a modulator modulates light from a source and images are created as a function of the modulation. A liquid crystal cell or liquid crystal display device may be such a modulator. A disadvantage of such modulating systems is the reduction in light output due to light blocking and/or absorption occurring in the modulator. To overcome such reduction in brightness, the intensity of the light source is sometimes increased, which draws additional energy, creates heat, requires a larger light source, etc.
Other display systems modulate reflective surfaces using a liquid crystal or cell. These reflective displays require an external light source directed at the display surface. Providing a light source capable of delivering sufficient luminous flux with an acceptable uniformity of the irradiance presents challenges in the context of an HMD. Thus, a need exists in the industry to address the aforementioned deficiencies and inadequacies.